Inhibiting copper plating in closed refrigeration systems



June 28, 1960 B. J. EISEMAN, JR

INHIBITING COPPER PLATING IN CLOSED REFRIGERATION SYSTEMS Filed Nov. 8, 1955 2 Sheets-Sheet 1 mcmwwmazoo mmmzwazoo INVENTOR BERNHARDT J. EISEMAN, JR.

BY WWW June 28, 1960 B. J. EISEMAN, JR

INHIBITING COPPER PLATING IN CLOSED REFRIGERATION SYSTEMS Filed Nov. 8, 1955 2 Sheets-She a 2 INVENTOR BERNHARDT J. EISEMAN JR.

/MKW $5 52: 2%: Hzztzciz ii $2: .23 w 2 miztzoi i m ATTORNEY INHIBITING COPPER PLATING IN CLOSEl) REFRIGERATION SYSTEMS Bernhardt J. Eiseman Jr. Wilmington Del. assignor- -to E. I. du Pont de Nemoins and Company,*Wilmington, Del., a corporation of Delaware Filed Nov. 8, 1955, Ser. No. 545,761 v 7 Claims. cmsz-ss This invention relates to a refrigerationprocess and, particularly, to a process for operating a-refrigeration system with a halogenated aliphatic hydrocarbon refrigerant and inhibiting copper plating in such system.

In the operation of refrigeration systems employing a halogenated aliphatic hydrocarbon containing chlorine, bromine, and/or fluorine as the refrigerant, corrosion and copper plating often develop. It is believed thatthe corrosion is due to breakdownof the refrigerant and the lubricant, resulting in part in the formation of reactive corrosion products. Such products and mixtures contact the mechanical elements and result in copper plating. Copper plating is the removal of copper from coppercontaining mechanical elements (such as copper tubing,

2,943,057 Patented June 28, 1960 terpolymers of acrylonitrile in which copolymers and terpolymers the acrylonitn'le predominates.

copper conductors and the like), and the deposition of such copper or of compounds having the appearance of copper, and of decomposition products on mechanical elements made of other metals (such as steel valves and pistons, bearings, and the like), causing failure of such mechanical elements and of the refrigeration system. 1

It is obvious that, if such corrosion and, particularly, such copper plating can be prevented or'- materially inhibited, the useful life of themechanical elements and of the refrigeration system can be considerably prolonged;

This problem has existed for many years, and those skilled in the art have proposed the addition of various substances to the refrigerants and to the lubricants to stabilize them or to otherwise eliminate the corrosion'and the copper plating, with varying degrees of success. Such substances have various defects, some being insufiicien tly effective and some being unstable or reactive and forming. undesirable solid or. semi-solid products resulting in sludges or gummy materials which can clog the capillary tubes and like elements. 4

It is an object of my invention to provide a new and improved process for operating refrigeration systems employing halogenated aliphatic hydrocarbon refrigerants. Another object is to provide such a process wherein copper plating is materially inhibited. A further object to provide such a process which involves contacting the refrigerant and the lubricant with a solid material which is effective to inhibit copper plating and which does not have the objectionable features of other materials pro; posed for the purpose. Other objects are to provide 'a novel process and to advance the Still otherobject s will appear hereinafter. I i The aboveand other'objects are accomplishedby' my invention which comprises operating a refrigeration system with a hydrocarbon lubricating oil and a refrigerant of the class consisting of 'chloroalkanes, chlorofluoroalkanes and bromofluoroalkanes, and contactingthe oil and the refrigerant with 'at least 0.3%*by weight, -based on the refrigerant, of a polymericmaterial-which'is solid at 300 F. andhas. a viscosity averagemolecular weight of at least about 20,000 and which is amember -of:the class consisting of ,polyacrylonitriles, copolymers and lit) vantages of providing a long wearing,'a'cid resi sting .1

; .There: is tendency for copper plating to occur in some refrigeration systems when there isrused therein refrigerantsof the class above *set forth. However," l 'have found that polymeric materials, of the class set forth -above,are very effective to materially-inhibit or delay such copper plating if the refrigerant and the oil are brought into contact therewith continuously or. intermittently at frequent intervals during. such operation. The precise mechanism through which such polymeric materials so function is not known. Such polymeric materials are known to the art,are solids, are insoluble in the refrigerants and in hydrocarbon lubricating oils, and do not react with the refrigerants or the oils. The polymeric materials appear to be stable under the conditions encountered in the refrigerationsystems and do not react to form objectionable products, such as sludges and gummy materials.- They are resistant to the, acids which may be generated in the refrigeration system, and remain effective, over long periods of time.

Polymeric materials useful in my process include the polymers of acrylonitrile itself (polyacrylonitriles), copolymers of acrylonitrile and a vinyl pyridine in which the acrylonitril'e predominates, and terpolymers of acrylonitrile, a vinyl pyridine, and a methylacrylate-andinter? polymers of acrylonitrile, a butylacrylate and methacrylic acid, said interpolymer being present as a binder with polyaci'ylonitrile fibers and as a component of an acrylic enamel containing" a phenol-formaldehyde resin, .the'

acrylonitrile predominating. Preferably, the acrylo 'titrile forms about 85% or more of the polymeric material. The vinyl pyridines consist of vinyl pyridine itself andits homologues, represented by Z-methyl-vinyl pyridine. p The methylacrylates are the methyl estersof acrylic .acid and its horhologues, such as methacrylicfacid.

are solid at temperatures up to-3 00l F; Usually, the polymer'ic materials will have a viscosity average molecular weight of 'at'. least" about: 20,000,; preferably vfrom about 20,000 to ab"out-500,000. The viscosity average jmolecular weight is the molecular weight that is determined" by measuring -the viscosit of "frac; tions of the" polymeric ,material in solu i0 deter'- inining'the osmotic pressureof each fraction from a: chart on which 'viscosities'are plotted against osmotic pressures and'determining the average molecular weight of each fraction from a second chart on which osmotici pressures are plotted against molecular weights; all in accordance; with the principles and methods described and discussed in the chapter by' Bagley and Mark appearing on pages through 109 in High Molecular Weight Organic Compounds edited by Burk and Grummitt and published in 1949 by Interscience Publishers, Inc. of New York.

' The polymericmaterials maybe in the form of coarse granules or pellets, preferably porous, but more usually will be in the form of coatings, sheets, fibers or fabric which, preferably, are attached to the refrigeration ap paratus in positions where they will be contacted by the refrigerant and the lubricant. For example, the polymeric material may be used to replace, at least in' part, theinsulation on the motor windings and the housing in the refrigeration apparatus. This has the additionalad sulation for the electrical system of the refrigeration apparatus. Also, the polymeric materials may be attached to the walls of the containers for the lubricant and the refrigerant. When used as coatings' or linings for parts subject ,to ,corrosiom they also. protect such parts from Also, the effective polymeric materials are, those. which I .inwhich .the .motoriis encased with oil.

corrosion. Further, the lubricant, or the refrigerant, or both can be passed through an absorption apparatus or filter containing the polymeric material. Still other methods of obtaining contact of the lubricant and the refrigerant with the polymeric material during operation of the refrigeration system will be apparent to those skilled. in the art.

A specific embodiment -of the .present invention in a hermetic'refrigeration system .is set forth .in the 'accom- 'panying drawing whereinfigure I depicts such a system The compressorreacts .on..the gaseous refrigerant, pushing it through lineAto the condenser where it becomes a liquid. The liquid .is :allowedto pass through the capillary-into the evaporator wherexthe liquid evaporates and in so doing reduces the temperature ofthe area around the evaporator coils. The gaseous refrigerant then passes through line B into the motor housing and then to the compressorwhere the cycleis repeated.

:Figure II is. an enlargementof themotor stator used in the motor of Figure I. This cut-away figure-shows the use of polyacrylonitrile fabric as a slot'liner and as a phase separator in the stator; said arrangement provides adequate contact-of the polyacrylonitrile with the refrigerant andlubricant to effectively reduce copper plating and the formation of gum deposits.

While a detectable decrease in copper plating can be observed when the polymeric material is present in a proportion of only 0.1% by weight based on the refrigerant, at least 0.3% by weight will be required for practicably significant results. Preferably, the polymeric material will be employed in a proportion of at least 2% by weight based on the refrigerant, and most usually about 3%. The maximum proportions of the polymeric material will be dictated solely by considerations of convenience, practicability and economy, since excessive proportions thereof are not harmful.

The refrigerants, which may be employed, are the chloroalkanes, the fluorochloroalkanes and the bromofluoroalkanes. Such refrigerants are represented by methyl chloride, methylene chloride, dichlorodifiuoromethane, tetrafluorodichloroethane, fiuorotrichloromethane, chlorotrifiuoromethane, mono chlorodifluoromethane and bromotrifluorometha'ne. "The process is especially adapted for use withtthe chlorofluoroalkanes and is preferably used with dichlorodifluoromethane.

The lubricant, which can be employed, may be any hydrocarbonlubricating oil having the viscosity. and other charatceristics required by the particular refrigeration ap' paratus employed. Usually, the lubricant wilLbe a high- 1y refined petroleum oil, but it may be composed,.in whole or .in part, of synthetic hydrocarbons, such as polyisobutylenes. .Also, the amount of the lubricant .will be that requiredlby the particular apparatus employed.

Because water may be formed duringthecontinued operation of-refrigeration systems and also seeps in from outside in some types of systems, an antifreeze agent, such as methanol, is often added to prevent ice formation from blocking the capillary tubes used for the expansion of the refrigerant. Such antifreeze agents appear to accelerate copper plating in such systems. However, I have found that the polymeric. materials, ems ployed'in my process, are also effective to materiallyinhibit copper plating in the presence of such antifreeze agents and such antifreeze agents-can be included in my process.

In order to more clearly illustrate=by invention, :preferred modes of carrying thesamelinto effect, and the advantageous resultsto be obtained thereby, .the following examples are given;

EXAMPLE 1 A one-eight horsepowerelectric motor is prepared in which the slot liners, phaseseparators, and wedges, which are normally made from celldlosic material, are I made from polyacrylonitrile cloth. The motor is then used in a hermetic compressor and the system operated at 130 to 135 F. ambient temperature. The compressor unit contains a refrigerant of dichlorodifluoromethane and a naphthenic base refrigerator lubricant (such as Suniso 3G Oil). After two months of continuous operation, the system is turned off, dismantled, and the compressor is examined. Very little copper plating is observed and there is no varnishing (formation of gum deposits).

T hissame testis appliedtotwohermetic compressors containingconventional motors,.i.e.,fthe;slot liners, phase separators, and wedges, and made of cellulosic material. At the end .of :theztwormonth .operating period at about 130;F. :ambient'temperature, one unitfails'due to seizing of the compressor bearings. On dismantling, an examination'of theccompressor ofboth units discloses large amounts of copper plating and varnish formation in the compressor bearings;

EXAMPLE 2 T Example '1 isrepeated with an .electric motor whose slot.1iners, phase separators and wedges, are of a nonwoven mat prepared from polyacrylonitrile fiber anda binder comprising an interpolymer prepared from acrylonitrile, butylacrylate and methacrylic acid in the weight ratio of 6323225. After two months of operation at about 130 F. ambient temperature, examination of the compressor discloses only slight discoloration of the metal parts (not copper plating) and the presence of an insignificant amount of gum deposit formation.

EXAMPLE 3 An electric motor is made in the conventional manner .(cellulosic slot liners, etc.) except that the wire used in the field coils is enameled with an acrylic wire enamel comprising .a phenol-formaldehyde resin (10%) and an interpolymer of acrylonitrile (90% The interpolymer is prepared from acrylonitrile, butylacrylate and methylacrylic :acid inthe-weight ratio .of 63:32:5. This motor is' 1thenrused in a hermetically sealed compressor system comprising a monochlorodifluoromethane refrigerant and a naphthenic base'refrigeration lubricant, such asfimiso 3G Oil. After two months of operation at about 130 F. ambient temperature, the unit is dismantled and examined. There is no evidence of copper plating or the formation of. gum .deposits.

When this same test is repeated with a motor containing field coils of wire enameled with a polyvinylbutyralresin, the compressor on dismantling, shows appreciable copper plating and .gum deposit formation.

EXAMPLE 4 A strip of copper, approximately 2% inches long by A'inch'wideby ,4 inch thick, and a strip of low carbon steel of 'similar size, separated from the copper by a piece of glass at each end, were tied together at each end with copper wire. Test strips, so prepared, were thenloaded intoglass pressuretubes. Into each tube, 25 cc. of a naphthenic base refrigeration lubricating oil and 2.6 g. of 'dichlorodifluoromethane were added. About 0.05 g. of polyacrylonitrile cloth, whose viscosity average molecular weight was about.33,000 to about 46,500, was introduced. Several tubes had no polyacrylonitrile and these were used forcontrol. The tubeswere then frozen in.liquid nitrogen ,and evacuated-to a few hundredths of a. millimeter ofmercury-pressure before sealing them. off

, by .fusing-the glass. lThetubes .wereallowedto warm fiberofthe kindused in Example 4 and with 'otherali- 5 in the tubes containing the polyacrylonitrile than in the controls, as may be seen from the following Table I:

similar test at l5 0' Cf showed the development of medium copper plating infour days in two control samples as compared to days and4l days for the tubes'containing the polyacrylonitrile.

' EXAMPLE 5 Experiments were carried out at 120 C.'as described in Example 4,with' varyingamounts of polyacrylonitrile phatic halide refrigerants.

The results are shown in the following tables: Y I a Table 11 [Retrigerantz Dichlorodifluoromethana] Days to Days to Amount oiInhibitorymg. Detectable Light L a Copper Copper Plating Plating Table III [Reirigerantz TetrafluorodichloroethaneJ Days to Days to Amount of Inhibitor, mg. Detectable Light Copper Copper Plating Plating None 7 l1 7 74 92 78 60 92 Table IV [Beirigerantz BromotrifluoromethaneJ Days to Days to Amount of Inhibitor, mg. Detectable Light Copper Copper Plating Plating Norm 5 22 Non 6 22 75 11 36 80. 11 36 i EXAMPLE 6 Experiments were carried out at 120 C. in the manner described in Example 4 with the following polymeric materials:

(A) Copolymer of acrylonitrile with 5% of vinyl 6 pyridine and a methylacrylatc and to have a viscosity average molecular weight of about 20,000 or more;

-(D) A commercial product sold under the trade name Dynel which is believed to be a copolymer of 40% acrylonitrile and 60% vinyl chloride and to have a'viscosity' average molecular weight of about 20,000 or more. (This product is included solely for purpose of comparison.) 1

The results of the t'ests are shown in the following Table -V:

' 7 Table V [Refrigerant Dichlorodifiuoromethane.)

Amount of Days for Days for Inhibitor Inhibitor, Detectable Light mg. Copper Copper Plating Plating It is apparent that polymeric material D, which contains vinyl chloride and less than acrylonitrile, has but little effect, insufiicient for practical use in my process. T

' EXAMPLE 7 78 mg. of polyacrylonitrile fiber like that of Example 5 were added to 2.6 g. of dichlorodifluoromethane containing 0.5 cc. of anhydrous methanol, and the test carried out at 120 C. in the presence of steel and copper strips as described in Example 4. A control test was carried out similarly. After 1 day, copper plating was observed in the control containing no inhibitor, whereas it require/d9 days and 16 days in duplicate tests to obtain observable copper plating when the polyacrylonitrile fiber was present. 7

Similar results were obtained when tet-rafluorodichloroethane and monochlorodifluoromethane were similarly tested. 7

The following Examples 8 and 9 are given for purposes ofv comparison:

EXAMPLE 8 0.08 gram each of gluta-ronitrile, adiponitrile, succino- 'nitrile, propionitrile, and benzonitrile were added to 2.6

pyridine, having a viscosity average molecular weight of grams of dichlorodifluoromethane and 2.5 cc. of refrigeration oil. Each mixture was then added to copper and steel strips as described in Example 4 and the system was heated overnight above 250 C. (The heating oven accidentally got out of control and an accurate temperature measurement could not be obtained.) In the morning, all of the test specimens showed extreme decomposition and showed considerably more copper plating than controls which did not contain any nitrile.

EXAMPLE 9 An experiment with phthalonitrile was run as described in Example 8 but at 120 C. At the end of 7 days, heavy copper plating had developed, whereas a control at the end of this time showed only a slight tarnish.

Examples 8 and 9 show that the property of inhibiting copper plating is not common to nitriles, but that the lower nitriles particularly are inoperative for such purpose. I a

The naphthenic base refrigeration lubricant utilized in Examples 1, 2 and 3 is Suniso 3G Oil whichhas a flash? point ASTM open cup 330340 F.; a pour point ASTM -35 F. maximum; Sligh oxidation 1020; floc test *--70 F. maximum; a density of 7.75 lbs. per gal. and an SUS viscosity at F. of ISO-to 160. ,For the other ex'g 'amples, the naphthenic base refrigeration lubricant 7 was Suniso'4G Oil whichthas a flash pointAsTMlopen cup 350--360 F.; a pour pointASTM -35? F..maxi- .mumpsligh oxidation .1020;'fioc .text 50 .maximum; .a density.of-7.627-lbs. pergalaand an-SUSviscosity .at 100 F. of '280 to.300.

.It will1be understood that the gprecedingsExamples .1

Qto 7 are, given for. illustrativepurposessolely, and. thatmy ing, which matetrials are not objectionable in-such systerns and do not react to produce objectionable substances; said materials are beneficial in that longer -motor-life-is obtained. .Mechanical failures of the refrigeration apparatus are thus greately decreased, maintenance costs are materially-lowered, and the-servicelivesof-therefrigeration systems are considerably :prolonged. Therefore, .it .is.apparent that my zinventiomconstitutestanrimportant advance in and contribution a to the :art.

This application is a continuation-in-part application of copending application Serial -No. 351,739, filed April 28, 1953, and now abandoned.

I claim:

1. 'A procas for inhibitingcopper platingina-tlosed refrigeration system containing steel and copper wherein said metals are contacted with a mixture of ahydrocarbon lubricating oil and a halogenated hydrocarbon refrigerant in the presence of at least 0.3% by weight,

.based on the refrigerant, .of atpolym'erictmaterial Which is solid at r3QO .-F.,- said gpolymericimaterial tbeing rpcsitioned in contact with said mixture, and has a viscosity average tmolecnlar weight -of at -least 10,000, said poly- .mericmaterial :being taken from the class consisting of 'polyacrylonitriles, copolymers, terpolyrners and interpolymers of 'acrylonitrile, the acrylonitrile component ;.predominating in said copolymers, terpolymers and interpolymers 'and, said polymeric material being substantially .insolubleimsaid.refrigerationsystem.

2. T-hcprocess of claim lwherein thelhalggcnated jhydrocarbon refrigerant -isa .chlorofiuoroalk ane. Y

3. The process of claim F1 where'inttheeacnylonitrile component forms about 85% of the; polymer-immaterial.

4. The process of claim'l whereinthe-polymei'ic material is polyacrylonitrile. 5 The process .of claim 1 'wherein r the .polymeric materialis a-copolyrner oiacrylomitrile,and-avinyl pyridine.

6. .Theprocess ofsclaim l whereinas'aid polymerict material is an'interpolymer.oftacrylonitrile azbutyl acrylate and methacrylic acid said inter-polymer being present as a binder with polyacrylonitrile fibers.

-7. The PIOCESS-fflf claim .1 whereinsaid solid polymeric material ,is nan interpolymer -,qf acrylonitrile, ya tbutyl acrylate andimethacrylic acid, ssaid :interpolymer. being present as acomponent of an; acrylic-enamel \T containing a phenol-formaldehyde resin. 7

References Cited in the file of this,,patent 'UNITED STATES -PA'TENT'S 2,060,728 :Fleischer .Nov. 10, 1936 2,243,104 Koethen May 27, 1941 2,524,590 'Boe Oct. 3, 1950 2,616,854 Fenske Nov. 4, 1952 2,653,133 Catlin Sept."2 2,1'9'53 

1. A PROCESS FOR INHIBITING COPPER PLATING IN A CLOSED REFRIGERATION SYSTEM CONTAINING STEEL AND COPPER WHEREIN SAID METAL ARE CONTACTED WITH A MIXTURE OF A HYDROCARBON LUBRICATING OIL AND A HALOGENATED HYDROCARBON REFRIGERANT IN THE PRESENCE OF AT LEAST 0.3% BY WEIGHT, BASED ON THE REFRIGERANT, OF A POLYMERIC MATERIAL WHICH IS SOLID AT 300*F. SAID POLYMERIC MATERIAL BEING POSITIONED IN CONTACT WITH SAID MIXTURE, AND HAS A VISCOSITY AVERAGE MOLECULAR WEIGHT OF AT LEAST 20,000, SAID POLYMERIC MATERIAL BEING TAKEN FROM THE CLASS CONSISTING OF POLYACRYLONITRILES, COPOLYMERS, TERPOLYMERS AND INTERPOLYMERS OF ACRYLONITRILE, THE ACRYLONITRILE COMPONENT PREDOMINATING IN SAID COPOLYMERS, TERPOLYMERS AND INTERPOLYMERS, AND, SAID POLYMERIC MATERIAL BEING SUBSTANTIALLY INSOLUBLE IN SAID REFRIGERATION SYSTEM. 